Support Guava version 21.0

Details

Description

Guava version 21.0 is an important version because it is the first with JDK 8 support (hence lambdas). Make sure that Calcite runs on it (on JDK 8 and later). Continue to support other versions of Guava as early as 14.0.1.

Compilation using mvn clean -Dguava.version=21.0 clean test on JDK8 currently yields many errors like the following: